Capacitor charging and discharging control



ept 25, 1945- c. E. SMITH ET AL CAPACITOR CHARGING AND DISCHARGING CONTROL Filed Feb. 12, 1943 2 Sheets-Sheet 1 INVENTORS C yc/e 507; #7 0/21 C/orence WITNESSES:

7 g l I ATTORN EY Sept. 25, 1945. c. SMITH ETAL 2,385,736

CAPACITOR CHARGING AND DISCHARGING CONTROL Filed Feb. 12, 1943 2 Shets-Sheet 2 ATTORNEY i invasion mates m a sygte initiated. as soon as possible after the rlischci'ge ling end discharging e. capacitor 2 is c letetl. tum ieletion to such apparatus accordingly, an object of our invention to a capacitor welt .1'. jei'ovicie 9. new and improved, cececito' folder.

.ln prior capes-tor welding systems of 5 Another object of invention is provide are aware, a. capacitor is charged. ii e 1361" status for racially chargingcegzecitoy to ncting current source through it rectifi r one. is desired mag Lltuoe. then discharged through the primary of e. Welds A for -M object oi our invention is PIQVMB og transformer. In some capacitor welders, no.-

eoperctus for rapidly charging it capacitor ireci magnitude Without overshooting.

" on is to provide for repiclly charging d magnitude and thereafter on cececitoi Weiclizig operations are performed singly, but in to welders a number of welding operations peiio mecl in rapid succession as long as switch, such as e cush-button switch, 1' i closed.

ivention is to pro- "sil y emerging c capacitor itho-ut overshooting and cotential charge on onstant.

short time il'lb e second. The capacitor must,

i Fepiclly. However, the cote must not overshoot (i. e. rise above and the" to the desired magnitude), Z101 sho not nticl choi e ilse to the desire; t

so. creen e sli 'htly higher veine cc-cause of current leakage. In other Words, tLe cepacltoz' must be Charged rapidly to desired potential ince'i'litucie end then maintained at a 3G tentielly constant potential until discharged.

L. e clificulty of accomplishing charging of th cooocito-r in this manner is increased beccue co nerciel conditions iequii'e e. variable capesitoi unit with 2. different potential choices for each ccpecitoi setting. These may vary from 55c to 3890 volts for e. capacitor of 12o to 2500 n1icrcfete/sis. There is, consequently, a tendeLey to overshoot the desired. potential magnitude v." '1 ertoin capacitors and to creep above the clesi negnitucie with others. Moreover, the potential any h3fif5fid capacitor tends to decrease beeuse current leakage when completely out off ZiOill the charging current source. Bificulty is --lso encountered because of the large transients oich may arise upon. initiation oi rapid rechergillg of the discharged capacitor.

Once the capacitor is charged, it must he clis charged through the weld ng transform-e1 oi'iin in at the proper instant with i'espect to other co ionel object of invention is to protus for charging and discharging a I eecitoi and. i itizitiz recharging thereof With me in which the charging g circuits are so inter coimected as of heiging immediately epacitor ging he 'lliilg proper s=- operations of t .e of the Welding with our invention, the power ed 0131 a source of polyphevse nt through a rectifier system.

"ow of current each phase erotions such as the positioning of he welding of the source to the capacitor. These valves are electrodes. In addition, the charging; and dls= endered conductive at substantially the same incherging circuits must be 50 related that rechargstain; ear y in each positive half ericd of the cor- ;cotentiels until the potential on the capacitor attains a, preselected ing of the capacitor does t begin until the W 1c capacitor has been coinslischer i but che magnitude slightly below the ultimate magnitude desired. As the potential charge on the capacitor increases above the preselected magnitude, the valves are rendered conductive gradually later in each succeeding positive half period of the corresponding phase potential until the ultimate desired magnitude is reached. The valves are prea vented from becoming conductive when the capacitor potential is at the ultimate desired mag nitude, and thus overshooting or creeping of the capacitor potential above the desired magnitude is avoided. However, should the capacitor potential decrease slightly because of a current leakage, the valves are rendered conductive very late in a positive half period of the corresponding phase potential to supply a small current to main= tain the capacitor at the desired potential.

The instant in a positive half period or" the corresponding phase potential at which any one of the valves is rendered conductive depends, of course, upon the characteristics of the potential impressed between the control electrode and cathode of the valve. A control circuit is provided for each valve and extends from the control elec-' trode to the cathode. An alternating potential having a sloping wave front and displaced in phase with respect to the corresponding phase potential across the anode and cathode of the valve is impressed in each control circuit. This alternating potential is, however, superimposed on a second potential which remains substantially constant until the capacitor potential attains the preselected magnitude and then decreases rapidly. The magnitude of the second potential while it remains constant is such that the valve is rendered conductive early in a half period of the corresponding phase potential. The rate of de-= crease of the second potential is proportional to the rate of increase of the capacitor potential but is sufiiciently rapid that the valve is not rendered conductive when the capacitor potential. is at the ultimate desired magnitude.

The discharge circuit or" the capacitor includes the primary or" a welding transformer and nitron connected in series therewith. After the capacitor is charged to the ultimate desired magnitude, the series connected ignitron'is rendered conductive, and the capacitor is discharged through the primary of the transformer. As the primary of the transformer is highly reactive, it tends to cause the capacitor to be charged in the inverse direction. To avoid such inverse charg ing, another ignitron is connected in shunt across the primary of the transformer. A firing circuit is provided to render the shunt connectedisnitron conductive upon a change in polarity across the primary of the transformer. Thus, the current which would charge the capacitor inversely is shunted through the shunt connected ignitron. This arrangement also permits the series corrnected ignitron to become non-conductive as soon as, or very shortly after, the capacitor is complete- 1y discharged. Therefore, recharging of the capacitor can be initiated while current is still flowing from the primary of the transformer through the shunt connected ignitron.

As the magnitude of the second potential lrnpressed in the control circuits of the rectifying valves is dependent upon the potential charge on the capacitor, it is apparent that these valves would ordinarily berendered conductive as soon nected ignitron is rendered conductive. This time interval is of such length as to permit the capacitor to he completely discharged, and thereafter the auxiliary means permits the valves to again become conductive. However, the valves are first rendered conductive very late in a positive half period of the corresponding phase po tential and then gradually earlier in succeeding positive half periods until they are rendered con ductive early in a positive half period. In this 7 manner large transients are avoided. Thereafter as the capacitor started to discharge. However,

auxiliary means are provided to maintain the valves non-conductive for a predetermined time interval following the instant that the series conthe valves are rendered conductive at substantially the same instant early in each positive half ceriod until the preselected capacitor potential magnitude is reached.

Another auxiliary means is provided which becomes efifective at the instant the shunt connected ignition is rendered conductive to initiate operation of sequence control and timing means which maintain prope" relation between the charging and discharging operations as Well as other operations of the welder, such as the positioning of the electrodes.

The novel features which we consider characteristic of our invention are set forth with particularity in the appended claims. The invention it: self, however, both as to organization and its method of operation, together with additional oblects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Figures 1 and 1A show the circuit connections of a capacitor welder embodying our invention; and

Fig. 2 is a graph illustrating the operation of a rectifier valve.

As shown in the drawings, a source 3 or" threephase alternating current is employed to supply charging current to power capacitors 5 through a circuit breaker l, a polyphase transformer and a rectifying system ill. The rectifying system includes a plurality of electric discharge valves i3, ill, ll, l9, ll and 23 of the arc-like type. These valves are connected in a well known manner so that current flows from the secondary windings or" the transformer 53 through the anodes cathodes 2? and 29, Si and and S5 and El of valves l3, l5 and ll to the capacitors 5 and then through the anodes and cathodes 39 and ll, of valves i8, 2%, and '23 back to the secondary windin s. The grid 63 of each or" valves i9, 2i and 23 is connected through a resistor (iii to its cathode 1% so that these valves are conductive whenever current is conducted through valves l3, l5 and ll. In other words, the flow of charging current is under the complete control of valves is, and ll, each of which controls current of a different one of the three phases.

The control circuit of valve l3 may be traced from the grid thereof through a grid resistor 3%, a secondary of a transformer 53, a resistor a portion of a voltage divider 5? to the intermediate tap Ell thereof, and from the intermediate tap through conductor 5! to the cathode 39 of the valve iii. The control circuit of valve may be similarly traced from its grid 63 through a grid resistor 55, a secondary 67 of another transformer 59, the resistor 55, a portion of the divider 5? to the intermediate tap 59 thereof, and from the intermediate tap 59 to the cathode 33 of the valve I5. The control circuit of valve ll may also be traced from its grid ll through a grid resistor l3, a secondary '15 of still another transformer ii, the resistor 55, a portion Swa ii-1s and. 5

in 0's rise used 1" the pent 33' we divider CELLUOGB s greath red deve 3 videfifo he catnode the DPGSiL-B resists resistors potential of 0 across bhE second pstemial the control electro" tive with resiectto control circuit is ivide maintain nega 'asssed case, the potential impressed across the resistor H9 in the control circuit of the pentode H3 must be set according to the ultimate potential charge to be placed on the capacitors 5.

An overvoltage protective device it? is also provided to prevent overcharging or the capacitors 5 should a failure occur in the charging system. This protective device includes an electric discharge valve MS of the arc-hke type hav ing an anode fill and cathode I53 connected in series with a push-button switch 55, the energlzing coil I57 of a relay E59, and the secondary llil of an auxiliary transformer i623 whose primary M55 is energized from the source 3. The control circuit of the valve i lil extends from the grid it? through a grid resistor 969 to an intermediate tap ill on the voltage divider i252 and from the positive terminal 62? of the divider through a phase shifting circuit liil energized from the source 3 through the auxiliary trans former I53 and thence to the cathode L53 of the valve. The phase shifting circuit H3 is arranged to impress an alternating potential leading by approximately 90 in phase the anode-cathode potential of the valve Hi9.

When the push-botton switch tee is closed, the valve Hill is immediately rendered conductive at the beginning of the positive half period of the source. As a result, the relay iiiil is energized, closing its contactor ill which completes a holding circuit around the push-button switch ltd. A second contactor l'lii of the relay i5?) is connected in series with a resistor till across the main capacitors 5 to form an emergency discharge circuit therefor. As long as the relay it?) is energized, the second contactor .i'lil remain open. The valve M9 is then conductive in each positive half period, and a capacitor E83 connected in shunt with the energizing coil iii? of the relay i59 maintains the relay energized dur ingthe intervening negative half periods. However, should the potential charge on the capacitors 5 rise to a dangerous magnitude, the po tential impressed in the control circuit of the valve M by the divider I25 becomes sufilciently negative to prevent the valve i 39 from being rendered conductive, in a positive half period. The relay 559 would then be deenergized, closing the emergency discharge circuit across the ca= pacitore.

The primary iild ofa welding transformer i8? is connected across the capacitors ii through an ignitron ltd and reversing contactors 59% or i913. As will be explained hereinafter, one or the other of the sets of reversing contactors lli or H93 is closed during each Welding operation.

A firing circuit for the ignition ltd in series with the welding transformer it? is provided and includes a circuit extending from the anode terminal 395 of the ignitron through the anode till and cathode use of another electric discharge firing valve 233 to the igniter 293 of the ignitron. The control circuit of the firing valve 293 includes a biasing potential source 2% tending to maintain the valve 2t! nonconductive and an impulse transformer 23? for supplying a poten= tial impulse to render the valve Zhl conductive. When the firing valve Zfil is rendered conduc tive, current flows from the positive plates Elli) of the capacitors 5 through the primary of the welding transformer 43?, the anodeltl and cathode Hi9 of the firing valve 2M and the igniter 283 and cathode 256 or" the ignitron ldii to the negative plates 2 of the capacitors As a result, the ignitron 555 is immediately ren aeaavsc dered conductive and, the capacitors 5 discharge through the primary m5 of the transformer I37. The secondary 293 of the transformer i8? is connected across the welding electrodes M5 and Eli which are at that time in engagement with the material Zlil to be welded.

Anotherignitron 2H is connected in shunt across the primary 5 85 of the welding transformer lill. Firing of this ignitron 22l is controlled by another electric discharge firing valve 223 of the arc-like type, which, in turn, is controlled by a small rectifier tube 225. An auxiliary capacitor 22? is connected across the anode 229 and cathode 23i of the firing valve 223 in a circuit which may be traced from the positive plate 233' of the capacitor 22? through the anode 22$ and cathode 23i of the firing valve 223, a resistor 235, igniter 23? and cathode 239 of the ignitron 225 to the negative plate 2 3i of the capacitor 227. The auxiliary capacitor ZfZ'i is originally charged from the source 3 through an auxiliary transformer 2&3, a rectifier and a resistor 267:.

The control circuit of the firing valve 228 may be traced from the grid 2539 through a grid resistor 25f, a source of substantially constant biasing potential 253, a resistor and the oath ode 23E and igniter 23! of the ignitron Hi to the cathode 23i of the valve. The resistor 255 is also connected across the primary we of the welding transformer it? through the small rectifying tube 225. When the main capacitors E5 discharges through the welding transformer primary ltd, the reactance of the primary tends to maintain the flow of current. In other words, after the capacitor potential decreases to zero, the decay of flux in the primary it? causes the polarity of the potential across the primary to reverse, and, therefore, the current continues to flow from the primary in the same direction in the capacitor discharge circuit. Ordinarily this would cause the power capacitors to he charged inversely. However, after the polarity of the po tential across the primary E85 reverses, the small rectifying tube 225 breaks down with but a very small inverse charge on the main capacitor and becomes conductive. Current immediately flows through the resistor 225 in the control circuit of the firing valve and the potential de veloped thereacross renders the firing valve 223 conductive. The auxiliary capacitor 22'l discharges through the firing valve 223' and the igniter 23? of the ignitron 22l connected in shunt with the primaryitfi of the welding transformer ml. This shunt connected ignitron 22! is immediately rendered conductive, and the current flowing from the primary $5 of the transformer it}? passes therethrough. In this manner, substantial inverse charging of the power capacitors 5 is prevented. When the shunt ignitron becomes conductive the potential across the series connected ignltron 68% is greatly reduced so that it becomes non-conductive. The discharge circuit for the power capacitors 5 is thus again i opened and in condition to permit recharging of the capacitors,

Because the pentode i i3 is responsive to the charge on the power capacitors 5, the initiation of the capacitor discharge through the welding transformer l iii would ordinarily cause the valves i3, i5, and il to again become conductive while the capacitors '5 are still discharging. Such a condition is obviously undesirable, and to avoid it, a timing circuit 25! is provided to maintain the pentode ii-3 non-conductive while the catial inverse charging of the capacitors and permitting the series connected ignitron N39 to become non-conductive.

Another electric discharge valve 325 of the arclike type has its anode 32? and cathode 32!! connected across a pair of resistors 339 and 333 through a normally closed contactor 335 of time delay relay 337i. contactor 339 of relay 299, another resistor ll, and the energizing coil 3% of another time delay relay 355. A direct-current potential is impressed across the pair of resistors 33! and 333 from an auxiliary source 367 through another resistor 389. The control circuit of the valve 325 extends from the grid 335i through a grid resistor 353, resistor 23%, the igniter 23? and cathode 239 of the shunt connected ignitron 22% and resistors 355 and 369 to the cathode 329. The potential across the resistor 349 from source 3%? ordinarily maintains the valve 325 non-conduc tive. However, when firing current is passed through the igniter 237 of the ignitronZZi, the momentary high potential across the igniter 23? and resistor 2355 developed by the current flow therethrough causes the valve 325 to become conductive, energizing time delay relay 365.

Another timing circuit Still is provided to maintain the welding electrodes in engagement with the material for an interval of time following thedischarge of the capacitators 5 which is commonly known in the Welding art as the hold time. The hold-time circuit comprises a potentiometer 359 connected directly across the source 3. When the circuit breaker 85 is originally closed. current flows from the source 3 through conductor 215, a portion of th potentiometer 359 to an intermediate tap 36E thereon, and from the intermediate tap 38! through a capacitor a resistor 355, the grid 36? and cathode oi an electric discharge valve Eli of the are like type and another resistor die and conductor 533i to the source. As the grid 36? and cathode 369 of the valve Sii act as a rectifier, the capacitor 363 is thus in a charged condition.

When the time delay relay 3% is energized, its contactor are completes a circuit from the oathode Btil of the valve Bit of the hold-timing cir cult 35'! through cont actor 3?? of relay con tactor 375 of relay 3%, and contactor Sill of relay 299 to conductor 27%. Thus, the potential of the source is removed from the auxiliary capacitor which discharges through a resistor 379 connected in parallel therewith. The anode 38E of the valve Eli is connected through a resistor 383 and the energizing coil 385 of time delay relay 295 and conductor 233i to the source. 4

Then when contactor 3'35 of relay 3 3i"; closes, the source 3 is connected across the anode 353i and cathode 35d of the valve Sil. However, the polarity of the charge across the auxiliary capacitor 3% maintains the valve non-conductive. After a predetermined time interval, the length of which is determined by the rate of discharge of the capacitor 363, the potential across the capacitor 363 decreases to a magnitude permitting the valve 3H to become conductive in each half cycle in which its anode Btl is positive. Current flowing through the valve 375 then energizes relay 295, and a capacitor 332 maintains the relay energized in the intervening negative half periods.

When relay 295 is energized, its contactor 3G7 closes an additional holding circuit around the push-button switch 29!. Contactor 2% of relay 295 opens the circuit through the energizing cell 297 of relay 299. When relay 299 is thus deenergized, its contactor 339 opens, but contactor 38$ of relay 365 maintains the anode circuit of the valve 325 closed; contactor 323 of relay 2539 opens the circuit through impulse transformers 207 and 273; contactor 30! opens the holding circuit around push button switch 29! but another holding circuit is already closed through contactor 383 of relay 295; contactor 3B3 opens the energizing circuit of relay 3; and contactor are opens the energizing circuit of the hydraulic valve 3H. When the hydraulic valve 3!? is deenergized, the head switch contactor 215 is closed, and the movable electrode M5 is soon thereafter raised out of engagement with the material 219 to be welded. Closing the head switch contactor 276 energizes the relay 279 whose contactor 283 closes a short circuit across the primary I of the transformer it? to prevent arcing at the electrode 215 when it is raised out of engagement with the material 2l9. Contactor 285 of relay 2'19 closes the charging circuit of the auxiliary capacitor 289.

Energization of relay 2% also closes contactcr 396 which completes a circuit from the source 3 through conductor 275i, contactor 351i, energizing coil Bill of relay 307! and conductor 28! to the source. Relay sill includes a ratchet and cam system 393 for operating contactor arm 3%. The arrangement is such that starting with the contactor arm 395 in the position shown with contacts 305 and 306 engaged, energization of the relay coil 39! causes the arm 395 to be lowered opening the circuit through contacts 385 and see and closing the circuit through contacts 395 and 397. Thus relay Bil is deenergized, open-- ingcontactors liii and the coil 399 of relay dot is energized. closing eontactors W3. Contacts 355 and 39? remain in engagement until relay Bill is deenergized and energized again. When relay till is energized again. the circuit through contactors 3% and 39? is opened and the circuit through contactors Sr'i and 3% is closed. Since rela iiiil is not energized again until after another welding operation, it is apparent that contactors lei are closed for one weldand contactors we are closed for the next weld. As the current flowing from capacitors 5 passes through the primary we in one direction with contactors .5 iii closed and in the opposite direction with core tactors 593 closed, saturation of the transformer iii? is avoided.

Another timing circuit 363, designated the offtime circuit, and similar in nature to the holdtime circuit 35?, is also provided. The oii-time circuit iii? comprises a potentiometer 6G5 energized from the source 3 and an auxiliary capacitor ill? originally charged from the source in a circuit extending from the source through conductor 2%, a portion of the potentiometer (105, to the intermediate tap M99, the auxiliary capacitor iifi'i. a resistor ll i, the grid M3 and cathode M5 of another electric discharge valve ill? of the are like type and resistor M9 to conductor 28!. The anode 32i of the valve M? is also connected to conductor 285 through a resistor Q23 and the energizing coil 4125 of time delay relay 337.

When relay 295 is energized by the hold-timing circuit 35?, its contactor iZ'i closes a circuit from the cathode 355 of the valve lii through contactor 327, a conductor 629, contactor 387 of relay 295 to conductor 275. Thus, the source potential is impressed across the anode 432i and cathode 615 of the valve lil. However, the polarity of the charge on the auxiliary capacitor id? is such that the valve ll? is maintained non-conductive.

when contactor. 421 is closed upon energization of relay 235, the source potential is removed from the auxiliary capacitor 401, which then discharges through a resistor 431 in shunt therewith. After a predetermined interval of time determined by the rate of discharge of the auxiliary capacitor 401, thepotential on the capacitor 401 decreases permitting thevalve 411 to become conductive in each half period of the source in which its anode 421 is positive to energize relay 331. A capacitor, 433 in shunt with coil 425 of the relay 331 maintains it energized during the intervening negative half periods.

When relay331 is energized, its contactor 335 opens the anode circuit of valve 325, causing relay 345 to be denergized. Contactor 311 of relay 331 opens the cathode circuit of the discharge valve 311 inv the hold-timing circuit 351 to render the valve 311 non-conductive. As a result, relay 235 is deenergized.

Upon deenergization of relay 235, the welding aparatus is in the same condition as it was when the push button switch 231 was first closed with the exception that the circuit through contact 305 is arranged to effect closure or contactors 133 instead of. contactors 131. If the push button switch 231 is still closed another welding operation takes place. It is to be noted that during a welding operation, the contactor 301 of relay 233 and contactor 331 of relay 235 complete hold; ing circuits around the push buttonswitch 231.

These holding circuits insure a complete welding operation even though the push button switch m rits-opened in the middle oi. the oper Therefore, welding operations continue to take place in rapid succession as long as push button switch 231 is held in closed position but the successionoi' welding operations is halted upon the completion of the next welding operation followhis opening of the push button switch.

sequence of events during repeated operations or the Welder may be briefly summarized. 'Assumingjcircuit' breakers! and 35 are closed so that main capacitor is charged and relay 2111 is energized "so that auxiliaryi'capacitor 233 is charged, closure of push button switch 231 first causes contactors 131 to'clos'e and electrode 215 to be moved downward into engagement with the material 213 tobe welded. Immediately thereafter the head switch 213 operates to deenergize relay 213 so that auxiliary capacitor 233 discharges through impulse transformers 231 and 213. Transformer 213 then initiates Operation of the timing circuit 251 to prevent a supply of charging current to the main capacitors 5 for a predetermined. interval 01' time At the same instant transformer 201 causes the series ignitron 133 to become conductive and the main capacitor 5 is discharged through the welding transformer 131 effecting a welding of the material 213.

As the potential of capacitors 5 drops to zero, the decay of iiux in primary 135 tends to produce a current to charge the capacitors 5 inversely. However, before a substantial inverse charging can be ,efiected, rectifier tube 225 breaks down causing the shunt ignitron 221 to become conductive. When the shunt ignitron 221 becomes conductive the series ignitron 133 becomes non-conductive. I

Just after the series lgnitron becomes non-conductive, the timin circuit 251 allows the controlling rectifying valves 13, 15 and 11 to become conductive late in a half period of the corresponding phase potential to initiate charging or the capacitor 5 while avoiding large transients. The

.a preselected magnitude.

instant in a positive halt period at which the valves 13,. 15 and 11 become conductive is rapidly advanced in the next few successive positive half periods until maximum charging current is supplied to the capacitor. The valves i3, i5 and 111 are then rendered conductive at substantially the same instant early in each successive positive half-period until the capacitors 5 are charged to Thereafter the valves 13, 15 and 11 are rendered conductive gradually later in each successive positive hali period to supply a gradually decreasing chargin current until the capacitor potential attains the ultimate desired magnitude, at which point the valves fail to become conductive. Should the capacitor potential decrease before the series ignitron becomes conductive the valves 13, 15 and 11 are rendered conductive late in a halt period to supply a small charging current to maintain the capacitor potential at the ultimate desired magnitude.

While the capacitors 5 are being recharged other circuits are reconditioning the discharge circuit. When the shunt ignitron 221 becomes conductive, valve 325 is rendered conductive to energize relay 345 and initiate operation of the hold time circuit 351. After the shunt ignitron 221 is rendered conductive the welding electrodes 215 and 211 areheld in engagement with the material 213, in accordance with well-known welding practice, for a time interval known as the hold-time and the length of which is here determined by the hold-time circuit 351. At the expiration of the hold-time period the electrode 15 is raised out of engagement with the material 213, the primary 135 of the welding transformers having been short circuited just prior thereto.

auxiliary capacitors 233 is charged and the relays are in the same condition as at the beginning of the first weld though in the meantime contactors 131 have been opened and contactors 133 closed to avoid saturation of the welding transformer. If the push button switch is still closed. a new weld is then made.

In a system actually constructed and tested as shown, WL-fi'l'? thyratrons were employed as rectifying valves 13, 15, l1, 13, 2t and 23. An R. C. A. 2A3 high-vacuum tube was employed as valve 31, and an R. C. A. 606 pentodc was used as the amplifying tube 113. The resistor 14 had a resistance of 1 million ohms; resistor 25 had a resistance of 10,000 ohms, a potential of 32 volts was impressed across resistance 113 and the capacitor 253 had a capacitance of 5 microiarads. Westinghouse WL688 ignltrons were employed as the series and shunt connected lg nitrons 133 and 221 in the discharge circuit of the capacitors 5. The firing valves 2M and 223 for the ignitrons 133 and 221 were Westinghouse WL-S'l'l thyratrons, and the rectifier-s 225 and 2-45 were R. C. A. 866-A tubes. A Westinghouse WL-SSO thyratron was employed as valve 323; a similar tube was employed as valve 161; and 9.. Westinghouse FLU-621 thyratron was used as valve 263.

Although we have shown and described certain specific embodiments of our invention, we

are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. In combination, a capacitor, means adapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said I capacitor, control means connected to said valve means for rendering said valve means conductive at substantially the same instant early in each positive pulsation of said source, and means associated with said control means and responsive to the potential charge on said capacitor for causing said control means to render said valve means conductive at an instant gradually later in each succeeding positive pulsation as said capacitor potential increases above-a preselected magnitude.

2. In combination, a capacitor, means adapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a predetermined critical value is impressed therein a positive pulsation of said source, and means responsive to the potential charge on said capacitor for impressing in said control circuit a potential which first rises above said critical value at sub-- stantially the same instant early in each positive pulsation while the capacitor potential is below a preselected magnitude and at an instant gradually later in each succeeding positive pulsation as the capacitor potential increases above said preselected magnitude.

3. In combination, a capacitor, means adapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a pre-' determined critical value is impressed therein in a positive pulsation of said source, and means adapted to impress in said control circuit a second periodic potential of the same periodicity as said source potential and having a sloping wave front superimposed on a third potential which is substantially constant while the capacitor potential is below a preselected magnitude and which gradually decreases as the capacitor potential increases above said preselected magnitude, the magnitude of said second and third potentials being such that the resultant potential in said control circuit first rises above said critical value at substantially the same instant early in each positive pulsation while said third potential is constant and at an instant gradually later in each succeeding positive pulsation as said third potential decreases.

4. In combination, a capacitor, mean adapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a, predetermined critical value is impressed means adapted to impress in said control circuit a second periodic potential of the same periodicity but displaced in phase relative to said source and having a sloping wave front superimposed on a third potential which is substantially constant while the capacitor potential is below a preselected magnitude and which gradually decreases as the capacitorpotential increases above said preselected magnitude;-

to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected'to said valve means and arranged to render said valve means conductive when a potential greater than a predetermined critical value is impressed therein in a positive pulsation of said source, and means adapted to impress in said control circuit a second potential which first rises above said critical value at substantially the same instant early in each positive pulsation while the potential charge on said capacitor is below a. preselected magnitude and at an instant gradually later in each succeeding positive pulsation as the capacitor potential increases above'said preselected magni- 40 tude, the rate of change of the instants at which said valve means is rendered conductive being dependent upon the rate of increase of said capacitor potential, said otential impressing means including means associated with said capacitor and eii'ective to amplify changes in the capacitor potential above said preselected magnitude only.

6; For use in charging a capacitor to a potential of a preselected magnitude from a source of periodically pulsating potential in circuit therewith, the combination comprising electric discharge valve means of the arc-like type interposed in circuit between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a predetermined critical value is impressed therein in a positive pulsation of said source, and means responsive to the potential charge on said capacitor and adapted to impress in said control circuit a potential which first rises above said critical value at substantially the same instant early in each positive pulsation while the capacitor potential is below a second preselected magnitude less than said first preselected magnitude and at an instant gradually later in each succeeding positive pulsation as the capacitor potential increases from said second preselected magnitude to said first preselected magnitude and which does not rise above said critical value when said ca- I pacitor potential is at said first preselected magnitude.

7. For use in charging a capacitor to a potential of a preselected magnitude from a source of 75 periodically pulsating potential in circuit theretherein in a positive pulsation of said source, and

5. In combination, a capacitor, means adapted" assures with, the combination comprising electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a predetermined critical value is impressed therein in a-positive pulsation of said source, and means adapted to impress in said control circuit a second periodic potential of the same frequency as said source and having a sloping wave front superimposed on a third potential which is substantially constant while the capacitor potential is below a second preselected magnitude less than said first preselected magnitude and which gradually decreases as said capacitor potential increases above said second preselected magnitude, the magnitude of said second and third potentials being such that the resultant potential first rises above said critical value at substantially the same instant early in each positive pulsation while said third potential is substantially constant and at an instant gradually later in each succeeding positive pulsation as said third potential decreases} said last means including means responsive to said capacitor potential for decreasing said third potential at a rate dependent upon the rate of increase or said capacitor potential in such manner that the resultant potential does not rise above said critical value when the capacitor potential is at said first preselected magnitude.

8. Apparatus according to claim 7 in which the means responsive to said capacitor potential for decreasing said third potential comprises elec tronic amplifying means in circuit with said capacitor and eilective to amplify changes in the capacitor potential above said second preselected magnitude only.

9. In combination, a capacitor, means adapted to function as a source of first periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means or the arc-like type interposed between said source and capacitor for con-- trolling the supply of charging current to said capacitor, control means associated with said valve means and comprising an electronic amplifying device having a pair of principal electrodes and a control electrode, an input circuit extending from said control electrode to one of said principal electrodes and including a resistance, means for impressing in said input circuit a second substantially constant potential of one polarity tending to make said control electrode positive, means for impressing in said input circuit a third potential of opposite polarity having a magnitude propontional to the potential charge on said capacitor whereby current flows in said input circuit when the resultant potential therein is of said one polarity, said resistance being of such dimensions that the potential between said control electrode and one principal electrode remains substantially constant while the resultant potential impressed in the input circuit is of said one polarity and varies in accordance with variations in said capacitor potential when said resultant potential is of said opposite polarity, means for adjusting the magnitude of said second potential so that the resultant potential remains of said one polarity until said capacitor potential attains a preselected magnitude, an output circuit connected across said principal electrodes and including means adapted to function as a source of a fourth substantially constant potential so that current how said first source depending upon the magnitude of said output circuit current.

10. In combination, a capacitor, means adapted to function as a source of polyphase alternating potential in circuit with said capacitor for supplying charging current thereto, rectifying means including an electric discharge valve of the arelike type interposed between each phase of said source and said capacitor .to control the supply of current of that phase to the capacitor, and control means for said valves comprising means arranged to render each valve conductive at an instant early in each positive half period of the corresponding phase potential and means associated with said last means and responsive to the potential charge on said capacitor for causing each of said valves to be rendered conductive at an iiistant gradually later in each succeeding positive half period of the corresponding phase potential as said capacitor potential increases above a preselected magnitude.

11. In combination, a capacitor, means adapted to function as a source of poly/phase alternating potential in circuit with said capacitor for supplying charsing current to said capacitor, rectifying means including an electric discharge valve of the arc-lilac type interposed between each phase of said source and said capacitor to control the sup-ply of current of that phase to the capacitor, each of said valves having a plurality of principal electrodes and a control electrode and adapted to be rendered conductive when a potential greater than a predetermined critical value is impressed between said control electrode and one of said principal electrodes in a positive half period of the corresponding phase potential, means adapted to impress between said control electrode and one principal electrode of each valve a second alternating potential of the same frequency as said corresponding ph is potential and having a sloping wave front, and means responsive to the po tential charge on said capacitor for also impressing between said control electrode and one principal electrode of each valve a third potential which is substantially constant while the capacitor potential is below preselected magnitude and which gradually decreases as the capacitor potential increases above said preselected magnitude, the magnitude of said second and third potentials being such that the total potential inipressd between said control electrode and one principal electrode first rises above said critical value at substantially the same instant early in each positive half period of the corresponding phase potential while said third potential is substantially constant and at an instant gradually later in each succeeding positive half period as said third potential decreases.

12. In combination, capacitor, means adapted to function as a source of current in circuit with said capacitor for supplying charging current thereto, valve means interposed between said source and capacitor for contr ling the supply of charging current to said capacitor, control means responsive to the potential charge on said capacitor for controlling the conductivity of said valve means so that said valve means is conductive when said capacitor potential is below a preselected magnitude and non-conductive when said capacitor potential is above said preselected mag 'from becoming conductive. for a predetermined time interval Iollowingthe closing of said discharge circuit.

13. In combination, a capacitor, means adapted to function as a source or current in circuit with said capacitor to supply charging current thereto, valve means interposed between said source and capacitor for regulating the magnitude of said charging current, control means associated with said valve means and responsive to the impression thereon of a potential less than a first predetermined magnitude to cause said valve means to permit a supply'of charging current at a substantially constant magnitude and each positive pulsation of said source, circuit means associated with said control means and effective upon the application thereto of a potential the magnitude of which is between a first preselected-value and a second preselected value greater than said first value to cause said control means to render said valve means conductive at an instant later in a positive pulsation, the greater the applied potential the later the'instant, and to prevent said control means from rendering said valve means conductive when the applied potential is above said second value, means for applying to said circuit means a second potential which varies in accordance with the potential charge on said capacitor, a normally open discharge circuit for said capacitor,

'-means operable after said capacitor is charged responsive to the impression thereon of a po-' tential greater than said first predetermined magnitude to efiect variation of said charging current'magnitude inversely as said impressed potential in such manner that said charging current recreases to zero when said impressed potential obtains a second predetermined magnitude, means for impressing on said control means a potential which varies according to the charge on said capacitor whereby said capacitor is charged to a magnitude corresponding to said current decreases to zero when said impressed potential, a normally open discharge circuit connected across said capacitor, means for eflecting closing of said discharge circuit until said capacitor is discharged, said discharge circuit reverting to its open condition after said capacitor is discharged and timing means rendered operable by said closing means and associated with said control means to prevent said valve means from becoming conductive for a predetermined time interval following the closing of said discharge circuit.

14. Apparatus according to claim 13 in which said timing means comprises means initiated by said closing means for impressing an additional potential onsaid control means of such magnitude during said predetermined interval of time that the total potential impressed on said control means is above said second predetermined magnitude.

15. Apparatus according to claim 13 in which said timing means comprises means initiated by said closing means for impressing an additional 0 which the means for applying the third potential potential on said control means of such char actor that the total potential impressed on said control means remains above said second predetermined magnitude for said predetermined interval of time, said additional potential decreasing gradually to zero following expiration of said predetermined time interval whereby recharging of said capacitor is initiated with a relatively low magnitude of charging current to avoid large transients.

16. In combination, a capacitor, means adapted to function as a source of periodically pulsating potential for supplying charging current to said capacitor, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, control means for rendering said valve means conductive at substantially the same instant early in to temporarily close said discharge circuit to disually but rapidly tc zero in such manner that. the resultant potential magnitude gradually decreases below said second value, whereby said valve means is rendered conductive late in a positive pulsation and thereafter gradually earlier in succeeding positive pulsations until said resultant potential is below said first value and then at substantially the same instant in each,

positive pulsation untilsaid second potential reaches said first value and then at an instant gradually later in each succeeding positive pulsation until said second potential attains said a second value. z

17. The combination according to claim 16in includes a second capacitor connected, to be charged from said source simultaneously with said first capacitor, means operable by said closing means for discharging said second capacitor, and means for developing a potential proportional to the discharge current from said capaci tor.

18. For use in supplying power to a reactive load, the combination comprising a capacitor in circuit with said load, a first ignitron connected in series between said capacitor and load, means connected across said capacitor for charging said capacitor, means for rendering said first ignitron conductive to discharge said capacitor through a said load, a second ignitron having 'a pair of principal electrodes connected in parallel relation'with said load and capacitor to conduct current resulting from the potential produced by a decay of the magnetic flux in said load after said capacitor is discharged, said second ignitron also having an ignition electrode, an electric discharge valve of the type which becomes conductive when a potential of a. relatively low magnitude is impressed thereacross, also connected in parallel relation with said load, said valve becoming conductive when said potential produced by the flux decay attains said relatively low magnitude, an auxiliary source of current, and means responsive to current flowing through said valve for conductively connecting said auxiliary source between said ignition electrode and one of said principal electrodes to render said second ignitron conductive.

19. Apparatus according to claim 18 in which said last means comprises a second electric dis,-

charge valve oi the arc-like type connected in circuit with said auxiliary source between said ignition electrode and said one principal electrode, and control means connected to said second valve and including biasing means normally tending to prevent said second valve from becoming conductive, said control means also including means responsive to current flowing through said first-named valve for counteracting said biasing means and thereby causing said second valve to become conductive.

20. For use in supplying power intermittently to a reactive load, the combination comprising a capacitor in circuit with said load. a first electric discharge valve of the arc-like type connected in series between said capacitor and load, means in circuit across said capacitor tor charging it to a preselected potential, control means operable to render said first valve conductive to eiiect discharge or said capacitor through said load, first-timing means initiated by said control means at the same time said first valve is rendered conductive for rendering said charging means ineflective for a first predetermined time interval thereafter, a second electric discharge valve of the arc-like type connected in shunt across said load, means responsive to the potential across said load resulting fromthe decay of magnetic flux therein after'said capacitor is discharged therethrough for rendering said sec-' ond valve conductive, said second valve being arranged to conduct the current produced by said load potential and thereby cause said first valve to become non-conductive and second timing means initiated by said load potential responsive means for eflecting operation or said control means a second predetermined time interval after said second valve is rendered conductive, said first and second timing means being so adjusted that said first interval does not expire until alter said capacitor is discharged and said second interval does not expire until after said capacitor is recharged.

21. In combination, a capacitor, means adapted to function as a source or periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, valve means interposed between said source and capacitor, control means for said valve means tending to cause said valve means to permit a supply 01 charging current of a substantially constant predetermined magnitude, means associated with said control means and responsive to the voltage across said capacitor for causing said valve means to reduce the magnitude of said charging current gradually as said capacitor voltage increases above a preselected value with said charging current being reduced to zero at a second predetermined value of capacitor voltage, a normally open discharge circuit connected across said capacitor, means for efiecting closing of said discharge circuit to substantially discharge said capacitor, said discharge circuit reverting to the open condition after said capacitor is substantially discharged, and means rendered operable by said closing means and associated with said control means for causing said valve means to prevent the supply of charging current for a predetermined time interval and thereafter eilfect a gradual increase of said charging current to said predetermined magnitude.

22. In combination, a capacitor, means adapted plying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor, control means connected to said valve means for rendering said valve means conductive at substantially the same instant early in each positive pulsation or said source, means associated with said control means and responsive to the voltage across said capacitor for causing said valve means to be rendered conductive at an instant gradually later in each succeeding positive pulsation as said capacitor voltage increases above a preselected value, a normally open discharge circuit connected across said capacitor, means for eflecting closing of said discharge circuit to substantially discharge said capacitor, said discharge clrcuit'reverting to said open condition after said capacitor is substantially discharged, and means rendered operable by said closing means and associated with said control means for preventing said valve means from becoming conductive tor a predetermined time interval and thereafter causing said valve means to be rendered conductive gradually earlier in successive positive pulsations from an instant late in a positive pulsation to said instant early in a positive pulsation. q 4

CLYDE E. SMITH. CLARENCE B. BTADUM. 

